1. Field of the Invention
The subject invention is in the field of sailboards, i.e. surfboards equipped for sailing with the operator standing essentially erect. The equipment comprises a sail attached to a mast and a boom. Specifically the invention is in the field of apparatus by which the boom is attached to the mast.
2. Prior Art
As the evolution of sailboards continues, the technology becomes more refined, aerodynamically and structurally. Aerodynamic and structural efficiency and cost effectiveness objectives rival those of aircraft. A key feature of the structural design is the means of attaching the boom to the mast. For convenience in transportation of the apparatus the boom is made readily attachable to and detachable from the mast. The point of attachment is adjustable along (i.e. up and down) the mast. The apparatus must be strong, light, flexible and as economically manufactured as practical. Part of this economy is achieved by avoiding requirements for close tolernces on the dimensions of parts of the apparatus. Avoiding close dimensional tolerances sets up special design problems, as will be evident from the prior art described and the following description of the invention.
The known prior art comprises the following U.S. patents, all related to the attachment of booms to masts of sailboards:
U.S. Pat. Nos. 4,319,536, 4,448,142, 4,334,488, 4,516,873, 4,436,047, 4,546,720.
U.S. Pat. No. 4,319,536 illustrates prior art in which the boom is lashed to the mast ("spar" in the patent) by a line, one end of which is tied onto the spar and the other end passes through holes in a fitting on the boom and the line is caught in a toothed V groove in the fitting. With this arrangement slippage of the boom along the mast during use has been frequently experienced and can only be remedied by completely undoing and redoing the attachment. It can be understood that this could be difficult if not impossible with the operator and sailboard in the water.
In the apparatus of U.S. Pat. No. 4,334,488 the boom is lashed to the mast by a "semi-elasticated circular strap." The term "circular" indicates that the strap is a loop. To fasten the boom to the mast the loop is attached to the mast and to a hook on the boom with the boom extending from the mast in a position 180.degree. from its intended final position and then the boom is moved in an arc in the plane of the boom and mast. This movement, in combination with the geometry of the boom attachment fitting, stretches the strap to hold the boom firmly against the mast. In this apparatus also, positioning and repositioning the point of attachment of boom to the mast is cumbersome and awkward, particularly in the water and more particularly because it is necessary to detach the sail from the boom.
U.S. Pat. No. 4,436,047 is not directed to attachment of the boom to the mast but, instead, to means for keeping the sail taut in spite of deflection of the boom under loads. However, it appears that the tension in the sail and sail tensioning mechanism would put unusual loads into the attachment of the boom to the mast. The forces tensioning the sail tend also to move the boom forward off the mast.
In the apparatus of U.S. Pat. No. 4,448,142, the friction which is intended to keep the boom positioned along the mast is produced by the tight fit between a V shaped notch in the fitting by which the boom is attached to the mast. The tight fit is produced by moving the boom from a position essentially parallel to the mast (the storage position) to a position essentially at a right angle to the mast. However, the position of the boom on the mast at which all this happens is determined by the positioning of a fixture which clamps on the mast and supports the pivot about which the boom moves in the action described for providing the friction force. Therefore, to adjust the point of attachment of the boom to the mast requires moving the boom into a position essentially parallel to the mast and loosening the fastening of the clamp. This is clearly a cumbersome process since it also involves detaching the boom and sail. Further, the successful use of the clamp requires maintaining the dimensional tolerances of the apparatus to a level not usually met in the manufacture of such apparatus for cost reasons.
The apparatus of U.S. Pat. No. 4,516,873 is similar to that of patent of U.S. Pat. No. 4,448,142 in that the force that produces the friction which is intended to hold the boom in a position along the mast is produced by camming action between the boom and the mast as the boom is moved from a position essentially parallel to the mast to a position essentially at a right angle to the mast. In this case the camming is applied to a "clamshell" clamp which surrounds the mast. In this apparatus also, relocating the point of attachment of the boom to the mast requires extensive manipulation of the boom and detaching the sail from the boom. Also, for successful operation, the dimensional tolerances must be held closer than is considered economically acceptable for this type of apparatus.
The apparatus of U.S. Pat. No. 4,546,720 also uses friction between a part with a V shaped notch and the mast. The notch is forced against and thereby positioned on the mast by the tension in the sail when the sail is attached to the boom. Therefore, repositioning a dislocated boom connection will require detaching the sail from the boom. This will prove cumbersome and frustrating for one person to accomplish since the fixture for positioning the boom on the mast is at one end of the boom and the sail attachment point is at the other.
It is considered that it can be understood from the above brief descriptions of prior art that there is a need for means for attaching the booms of sailboards to the masts which provides simple, convenient attachment of the boom to the mast and simple, convenient adjustment and readjustment of the position at which the boom is attached. Further, the need calls for the apparatus to be easily managed by one person, even if the person and sailboard are in the water. Still further, it is required that the apparatus not require close dimensional tolerances for successful performance.